using System;
using System.IO;
using System.Reflection;
using XWorld.Framework;

namespace XWorld.Server.Host
{
    public sealed class GameModuleLoader
    {
        private readonly string _publicKeyPem;

        public GameModuleLoader(string publicKeyPem = null)
        {
            _publicKeyPem = publicKeyPem;
        }

        public LoadedGameModule Load(string gamesRoot, string gameId, int version)
        {
            string moduleDir = Path.Combine(gamesRoot, gameId, version.ToString());
            if (!Directory.Exists(moduleDir))
                throw new DirectoryNotFoundException($"游戏模块目录不存在: {moduleDir}");

            if (_publicKeyPem != null)
                VerifySignature(moduleDir);

            var manifest = GameManifest.Load(Path.Combine(moduleDir, "game.json"));
            if (manifest.GameId != gameId || manifest.Version != version)
                throw new InvalidDataException(
                    $"game.json 与目录不符: 期望 {gameId} v{version}, 实际 {manifest.GameId} v{manifest.Version}");

            if (manifest.MinFrameworkVersion > XWorld.Framework.FrameworkInfo.Version)
                throw new InvalidOperationException(
                    $"小游戏要求最小框架版本 {manifest.MinFrameworkVersion}，当前框架 {XWorld.Framework.FrameworkInfo.Version}，请更新框架后重试");

            string serverDll = Path.Combine(moduleDir, manifest.ServerAssembly);
            if (!File.Exists(serverDll))
                throw new FileNotFoundException($"服务端入口 DLL 不存在: {serverDll}");

            var alc = new GameModuleAlc($"{gameId}@{version}", moduleDir);
            try
            {
                Assembly entryAsm = alc.LoadEntry(serverDll);
                Type entryType = entryAsm.GetType(manifest.ServerEntryType);
                if (entryType == null)
                    throw new InvalidOperationException(
                        $"在 {serverDll} 中找不到入口类型 {manifest.ServerEntryType}");
                if (!typeof(IGameServerRoom).IsAssignableFrom(entryType))
                    throw new InvalidOperationException(
                        $"{manifest.ServerEntryType} 未实现 IGameServerRoom");

                Func<IGameServerRoom> factory = () => (IGameServerRoom)Activator.CreateInstance(entryType);
                return new LoadedGameModule(gameId, version, alc, factory);
            }
            catch
            {
                alc.Unload(); // 失败路径：立刻卸载，避免遗留锁住 DLL 的 collectible ALC
                throw;
            }
        }

        // 注意：签名清单仅覆盖 ServerAssembly/CoreDll/game.json（当前小游戏 = Core+Server 两 DLL，完整覆盖）。
        // 若将来小游戏带私有第三方 DLL，发布工具(PublishLayout)与此处校验须同步把它们纳入清单。
        private void VerifySignature(string moduleDir)
        {
            string filesTxt = Path.Combine(moduleDir, "files.txt");
            string sigPath = Path.Combine(moduleDir, "files.txt.sig");
            if (!File.Exists(filesTxt) || !File.Exists(sigPath))
                throw new InvalidOperationException($"缺少签名清单，拒绝加载: {moduleDir}");
            var fm = XWorld.PublishTool.FilesManifest.Parse(File.ReadAllText(filesTxt));
            if (!XWorld.PublishTool.ManifestSigner.Verify(fm.Digest(), File.ReadAllBytes(sigPath), _publicKeyPem))
                throw new InvalidOperationException($"签名验证失败，拒绝加载: {moduleDir}");
            foreach (var kv in fm.Entries)
            {
                string p = Path.Combine(moduleDir, kv.Key);
                if (!File.Exists(p) || XWorld.PublishTool.Md5Util.OfFile(p) != kv.Value.Md5)
                    throw new InvalidOperationException($"文件 md5 不符或缺失，拒绝加载: {kv.Key}");
            }
        }
    }
}